Semiotics and signs: why do we use the colours we do?

When it comes to health and safety signs, you’ll no doubt notice that different types of signs have different shapes: triangular or diamond shapes for warning signs, round for prohibitive signs and so on. But have you stopped to think about the different colours that are used in safety signs and why they are actually used?

The choice of colours is no accident: it’s all do to with semiotics – the science behind how symbols and signs communicate messages to those who see them. When it comes to warning signs and other safety signs, colour has a massive impact on the way in which the brain interprets what it sees.

Prohibition signs – such as “stop” and “no smoking” signs – are always red. This is partly because our brains associate red with things like blood and danger, telling us that something isn’t right. But there are other reasons too: the colour red weakens the least when travelling through the air and travels the furthest through weather conditions such as rain and fog, and there are receptors in our eyes that are more sensitive to red than to other colours, making these signs stand out.

Warning signs, on the other hand, are yellow; used on signs such as those that make us aware of toxic substances. Yellow is one of the colours that is most visible to the human eye, and we associate the colour with a potential hazard (think of the red, yellow/amber, green warning light system). In addition, yellow is known to draw attention, making it the perfect choice for signs that need to be read.

Instructional and mandatory signs, such as those signalling a hard hat area, are blue. Blue is a powerful colour and one that has connotations of wisdom and intelligence, making it perfect for displaying mandatory information.

Finally, the colour green is used for signs highlighting safe conditions, such as a fire/emergency exit. Why? Because green, in our minds, signals freedom and peace, and can blend in well while still being easily recognisable when needed.

While you may not have previously questioned the use of different colours in health and safety signs, the study of semiotics shows that they’re there for good reason.